WASHINGTON (Reuters) - The White House race between U.S. President Barack Obama and Republican challenger Mitt Romney remained a cliffhanger in four critical states that may tip the outcome of Tuesday's election, according to a Reuters/Ipsos poll released on the eve of the election.

Incumbent Obama maintained a 4 percentage point lead in Ohio, and slimmer leads in Virginia and Colorado, while Romney led by 1 percentage point in Florida, the poll showed.

In perhaps the most pivotal state of Ohio, Obama had the support of 50 percent of likely voters, while Romney was at 46 percent. On Sunday, Obama led 48 percent to 44 percent.

In Virginia, Obama held a slim lead of 48 percent to Romney's 46 percent among likely voters.

In Colorado, Obama was also at 48 percent, a nose ahead of Romney's 47 percent.

Romney had a slight lead in Florida, where 48 percent of likely voters sided with the Republican and 47 percent backed the Democrat Obama.

All of the results are within the polls' credibility intervals, a tool used to account for statistical variation in Internet-based polling.